In recent years, image recording apparatuses (or signal processing apparatuses or image data generation apparatuses) such as digital video cameras and digital (still) cameras are widely used in the ordinary household. Such image recording apparatuses generally have a zoom function capable of continuously changing the photographing view angle from a wide-angle mode to a telephoto mode by user operation. Many image recording apparatuses have even an electrical zoom function of electronically variably magnifying photographing image data in addition to a conventional optical zoom function using a zoom lens optical system.
FIG. 26 is a block diagram showing the schematic arrangement of a conventional image recording apparatus having an optical zoom function and an electrical zoom function. Referring to FIG. 26, a lens optical system 2301 includes an optical lens which forms an image of incident light on an image sensing element 2302, an aperture, a focus controller, various kinds of optical filters, and a driving mechanism for them. The lens optical system 2301 can execute optical zoom for optically changing the view angle and includes a driving mechanism for it.
The above-described optical mechanism in the lens optical system 2301 of the image recording apparatus shown in FIG. 26 is a common mechanism, and a description thereof will be omitted. The image sensing element 2302 converts the optical signal of an image formed on the light-receiving surface by the lens optical system 2301 into an electrical signal. For example, a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) sensor are known.
An A/D (Analog-to-Digital conversion) circuit 2303 converts the image sensing signal, which has been converted into an electrical signal by the image sensing element 2302, into digital image sensing data (to be referred to as image sensing data hereinafter). A memory 1 (2304) stores the image sensing data converted by the A/D circuit 2303. At this point of time, the image sensing data is digital data in an output format unique to the image sensing element (the output format changes depending on the pixel array and the color filter array). A camera signal processing circuit 2305 executes various processing operations for converting the image sensing data supplied from the memory 1 (2304) into image data. A zoom control circuit 2307 controls an optical zoom control circuit 2306 in accordance with input from a zoom operation key 2310. The zoom control circuit 2307 also controls an enlargement processing circuit 2309 through a switch 2308. The optical zoom control circuit 2306 controls the lens optical system 2301 to perform optical zoom under the control of the zoom control circuit 2307. The enlargement processing circuit 2309 executes electrical zoom processing under the control of the zoom control circuit 2307. That is, the zoom control circuit 2307 allows optical zoom or electrical zoom processing.
An electrical zoom ON/OFF switch 2311 turns on/off the electrical zoom function. When the electrical zoom ON/OFF switch 2311 is OFF, the switch 2308 is turned off to inhibit the enlargement processing circuit 2309 from executing enlargement processing. When the electrical zoom ON/OFF switch 2311 is ON, the switch 2308 is turned on to cause the enlargement processing circuit 2309 to execute enlargement processing. The electrical zoom ON/OFF switch 2311 is prepared for users who dislike a degradation in image quality due to enlargement by electrical zoom so that photographing can be executed while setting the zoom control mode for only optical zoom.
A memory 2 (2312) stores image data which has undergone camera signal processing and enlargement processing. A recording signal processing circuit 2313 executes compression-coding, recording format generation, error-correcting coding, or recording modulation coding for the image data read out from the memory 2 (2312). A recording medium 2314 records the image data processed by the recording signal processing circuit 2313.
The optical zoom and electrical zoom operations in the image recording apparatus shown in FIG. 26 will be described next.
FIG. 27 is a view showing the optical zoom and electrical zoom operations in the image recording apparatus shown in FIG. 26. A frame 2401 indicates the range of the object (including a tree, a skier, and a cloud) of image data stored in the memory 1 (the frame 2401 indicates the view angle). The frame 2401 becomes large as the optical zoom shifts to the wide-angle side. More specifically, in a zoom control region 2406 for optical zoom, when the lens optical system 2301 is controlled to the maximum wide-angle state, the frame 2401 becomes large. At that view angle, a wide-angle image 2403 is obtained. Accordingly, the image data of the object indicated by the wide-angle image 2403 is stored in the memory 1. In the zoom control region 2406, when the lens optical system 2301 is controlled to the maximum telephoto state, a telephoto image 2404 is obtained at the view angle corresponding to the frame 2401. Accordingly, the image data of the object indicated by the telephoto image 2404 is stored in the memory 1. As described above, the image recording apparatus shown in FIG. 26 executes the zoom operation by changing the photographing view angle (the range of the frame 2401) by controlling the lens optical system 2301.
On the other hand, in a zoom control region 2407 for electrical zoom, a partial area indicated by a frame 2402 is extracted and enlarged from the image data of the object within the frame 2401 in the maximum telephoto state, thereby obtaining an electrical zoom image 2405.
At this time, the image quality degrades to some extent in electrical zoom processing, as described above. Especially, when the magnification ratio of electrical zoom is high, the image quality largely degrades. To prevent this, the magnification ratio of electrical zoom is generally limited by defining an upper limit value.
There is also disclosed an information recording apparatus (image recording apparatus) capable of preventing any unintentional degradation in image quality by excessive electrical zoom processing (e.g., Japanese Patent Laid-Open No. 2001-197347). In this apparatus, when electrical zoom processing may cause an undesirable degradation in image quality, the electrical zoom processing is restricted, or a warning is displayed.
More specifically, the information recording apparatus comprises an image sensing unit which senses an image, and an electrical zoom processing unit which acquires a selected image within a predetermined range from the image obtained by the image sensing unit and converts the selected image into an output image having a predetermined number of pixels. The electrical zoom processing unit has a selection range condition setting function of setting a condition to be satisfied by the selected image by referring to the number of pixels of the output image. The apparatus further comprises a notification unit which notifies a user that the condition is not satisfied when the selected image does not satisfy the condition. With the above-described arrangement, when electrical zoom processing may cause an undesirable degradation in image quality, the electrical zoom processing can be restricted, or a warning can be displayed.
Some signal processing apparatuses and image data generation apparatuses, which have come along in recent years, record reduced image data smaller than the image size of the image sensing element in some recording modes, as in the moving image photographing mode of a digital video camera having a still image photographing function. In such signal processing apparatuses and image data generation apparatuses, even when photographing is performed by setting for only optical zoom, the image data is further reduced electronically and recorded in some recording modes. That is, setting for electrical zoom is not done in consideration of the electronic reduction. In other words, it is inconsistent with the primary purpose of the photographing mode which prevents, by electrical zoom ON/OFF setting, the degradation in image quality by enlargement processing.